cache_handler(3) net-snmp cache_handler(3)NAME
cache_handler -
Maintains a cache of data for use by lower level handlers.
Functions
netsnmp_cache * netsnmp_cache_get_head (void)
get cache head
netsnmp_cache * netsnmp_cache_find_by_oid (const oid *rootoid, int
rootoid_len)
find existing cache
netsnmp_cache * netsnmp_cache_create (int timeout, NetsnmpCacheLoad
*load_hook, NetsnmpCacheFree *free_hook, const oid *rootoid, int
rootoid_len)
returns a cache
int netsnmp_cache_free (netsnmp_cache *cache)
frees a cache
unsigned int netsnmp_cache_timer_start (netsnmp_cache *cache)
starts the recurring cache_load callback
void netsnmp_cache_timer_stop (netsnmp_cache *cache)
stops the recurring cache_load callback
netsnmp_mib_handler * netsnmp_cache_handler_get (netsnmp_cache *cache)
returns a cache handler that can be injected into a given handler
chain.
netsnmp_mib_handler * netsnmp_get_cache_handler (int timeout,
NetsnmpCacheLoad *load_hook, NetsnmpCacheFree *free_hook, const oid
*rootoid, int rootoid_len)
returns a cache handler that can be injected into a given handler
chain.
int netsnmp_cache_handler_register (netsnmp_handler_registration
*reginfo, netsnmp_cache *cache)
functionally the same as calling netsnmp_register_handler() but
also injects a cache handler at the same time for you.
int netsnmp_register_cache_handler (netsnmp_handler_registration
*reginfo, int timeout, NetsnmpCacheLoad *load_hook,
NetsnmpCacheFree *free_hook)
functionally the same as calling netsnmp_register_handler() but
also injects a cache handler at the same time for you.
NETSNMP_STATIC_INLINE char * _build_cache_name (const char *name)
void netsnmp_cache_reqinfo_insert (netsnmp_cache *cache,
netsnmp_agent_request_info *reqinfo, const char *name)
Insert the cache information for a given request (PDU).
netsnmp_cache * netsnmp_cache_reqinfo_extract
(netsnmp_agent_request_info *reqinfo, const char *name)
Extract the cache information for a given request (PDU).
netsnmp_cache * netsnmp_extract_cache_info (netsnmp_agent_request_info
*reqinfo)
Extract the cache information for a given request (PDU).
int netsnmp_cache_check_expired (netsnmp_cache *cache)
Check if the cache timeout has passed.
int netsnmp_cache_check_and_reload (netsnmp_cache *cache)
Reload the cache if required.
int netsnmp_cache_is_valid (netsnmp_agent_request_info *reqinfo, const
char *name)
Is the cache valid for a given request?
int netsnmp_is_cache_valid (netsnmp_agent_request_info *reqinfo)
Is the cache valid for a given request? for backwards
compatability.
int netsnmp_cache_helper_handler (netsnmp_mib_handler *handler,
netsnmp_handler_registration *reginfo, netsnmp_agent_request_info
*reqinfo, netsnmp_request_info *requests)
Implements the cache handler.
void release_cached_resources (unsigned int regNo, void *clientargs)
run regularly to automatically release cached resources.
Detailed Description
Maintains a cache of data for use by lower level handlers.
This helper checks to see whether the data has been loaded 'recently'
(according to the timeout for that particular cache) and calls the
registered 'load_cache' routine if necessary. The lower handlers can
then work with this local cached data.
A timeout value of -1 will cause netsnmp_cache_check_expired() to
always return true, and thus the cache will be reloaded for every
request.
To minimze resource use by the agent, a periodic callback checks for
expired caches, and will call the free_cache function for any expired
cache.
The load_cache route should return a negative number if the cache was
not successfully loaded. 0 or any positive number indicates successs.
Several flags can be set to affect the operations on the cache.
If NETSNMP_CACHE_DONT_INVALIDATE_ON_SET is set, the free_cache method
will not be called after a set request has processed. It is assumed
that the lower mib handler using the cache has maintained cache
consistency.
If NETSNMP_CACHE_DONT_FREE_BEFORE_LOAD is set, the free_cache method
will not be called before the load_cache method is called. It is
assumed that the load_cache routine will properly deal with being
called with a valid cache.
If NETSNMP_CACHE_DONT_FREE_EXPIRED is set, the free_cache method will
not be called with the cache expires. The expired flag will be set, but
the valid flag will not be cleared. It is assumed that the load_cache
routine will properly deal with being called with a valid cache.
If NETSNMP_CACHE_PRELOAD is set when a the cache handler is created,
the cache load routine will be called immediately.
If NETSNMP_CACHE_DONT_AUTO_RELEASE is set, the periodic callback that
checks for expired caches will skip the cache. The cache will only be
checked for expiration when a request triggers the cache handler. This
is useful if the cache has it's own periodic callback to keep the cache
fresh.
If NETSNMP_CACHE_AUTO_RELOAD is set, a timer will be set up to reload
the cache when it expires. This is useful for keeping the cache fresh,
even in the absence of incoming snmp requests.
Here are some suggestions for some common situations.
Cached File: If your table is based on a file that may periodically
change, you can test the modification date to see if the file has
changed since the last cache load. To get the cache helper to call the
load function for every request, set the timeout to -1, which will
cause the cache to always report that it is expired. This means that
you will want to prevent the agent from flushing the cache when it has
expired, and you will have to flush it manually if you detect that the
file has changed. To accomplish this, set the following flags:
NETSNMP_CACHE_DONT_FREE_EXPIRED NETSNMP_CACHE_DONT_AUTO_RELEASE
Constant (periodic) reload: If you want the cache kept up to date
regularly, even if no requests for the table are received, you can have
your cache load routine called periodically. This is very useful if you
need to monitor the data for changes (eg a LastChanged object). You
will need to prevent the agent from flushing the cache when it expires.
Set the cache timeout to the frequency, in seconds, that you wish to
reload your cache, and set the following flags:
NETSNMP_CACHE_DONT_FREE_EXPIRED NETSNMP_CACHE_DONT_AUTO_RELEASE
NETSNMP_CACHE_AUTO_RELOAD
Function Documentation
int netsnmp_cache_check_and_reload (netsnmp_cache * cache)
Reload the cache if required.
Definition at line 420 of file cache_handler.c.
int netsnmp_cache_check_expired (netsnmp_cache * cache)
Check if the cache timeout has passed. Sets and return the expired
flag.
Definition at line 405 of file cache_handler.c.
netsnmp_cache* netsnmp_cache_create (int timeout, NetsnmpCacheLoad *
load_hook, NetsnmpCacheFree * free_hook, const oid * rootoid, int
rootoid_len)
returns a cache
Definition at line 146 of file cache_handler.c.
netsnmp_cache* netsnmp_cache_find_by_oid (const oid * rootoid, int
rootoid_len)
find existing cache
Definition at line 130 of file cache_handler.c.
int netsnmp_cache_free (netsnmp_cache * cache)
frees a cache
Definition at line 189 of file cache_handler.c.
netsnmp_cache* netsnmp_cache_get_head (void)
get cache head
Definition at line 122 of file cache_handler.c.
netsnmp_mib_handler* netsnmp_cache_handler_get (netsnmp_cache * cache)
returns a cache handler that can be injected into a given handler
chain.
Definition at line 282 of file cache_handler.c.
int netsnmp_cache_handler_register (netsnmp_handler_registration * reginfo,
netsnmp_cache * cache)
functionally the same as calling netsnmp_register_handler() but also
injects a cache handler at the same time for you.
Definition at line 330 of file cache_handler.c.
int netsnmp_cache_helper_handler (netsnmp_mib_handler * handler,
netsnmp_handler_registration * reginfo, netsnmp_agent_request_info *
reqinfo, netsnmp_request_info * requests)
Implements the cache handler.
next handler called automatically - 'AUTO_NEXT'
next handler called automatically - 'AUTO_NEXT'
next handler called automatically - 'AUTO_NEXT'
Definition at line 455 of file cache_handler.c.
int netsnmp_cache_is_valid (netsnmp_agent_request_info * reqinfo, const
char * name)
Is the cache valid for a given request?
Definition at line 437 of file cache_handler.c.
netsnmp_cache* netsnmp_cache_reqinfo_extract (netsnmp_agent_request_info *
reqinfo, const char * name)
Extract the cache information for a given request (PDU).
Definition at line 385 of file cache_handler.c.
void netsnmp_cache_reqinfo_insert (netsnmp_cache * cache,
netsnmp_agent_request_info * reqinfo, const char * name)
Insert the cache information for a given request (PDU).
Definition at line 368 of file cache_handler.c.
unsigned int netsnmp_cache_timer_start (netsnmp_cache * cache)
starts the recurring cache_load callback
Definition at line 226 of file cache_handler.c.
void netsnmp_cache_timer_stop (netsnmp_cache * cache)
stops the recurring cache_load callback
Definition at line 261 of file cache_handler.c.
netsnmp_cache* netsnmp_extract_cache_info (netsnmp_agent_request_info *
reqinfo)
Extract the cache information for a given request (PDU).
Definition at line 397 of file cache_handler.c.
netsnmp_mib_handler* netsnmp_get_cache_handler (int timeout,
NetsnmpCacheLoad * load_hook, NetsnmpCacheFree * free_hook, const oid *
rootoid, int rootoid_len)
returns a cache handler that can be injected into a given handler
chain.
Definition at line 311 of file cache_handler.c.
int netsnmp_is_cache_valid (netsnmp_agent_request_info * reqinfo)
Is the cache valid for a given request? for backwards compatability.
for backwards compat
netsnmp_cache_is_valid() is preferred.
Definition at line 448 of file cache_handler.c.
int netsnmp_register_cache_handler (netsnmp_handler_registration * reginfo,
int timeout, NetsnmpCacheLoad * load_hook, NetsnmpCacheFree *
free_hook)
functionally the same as calling netsnmp_register_handler() but also
injects a cache handler at the same time for you.
Definition at line 343 of file cache_handler.c.
void release_cached_resources (unsigned int regNo, void * clientargs)
run regularly to automatically release cached resources. xxx - method
to prevent cache from expiring while a request is being processed (e.g.
delegated request). proposal: set a flag, which would be cleared when
request finished (which could be acomplished by a dummy data list item
in agent req info & custom free function).
Definition at line 608 of file cache_handler.c.
Author
Generated automatically by Doxygen for net-snmp from the source code.
Version 5.5 23 Sep 2009 cache_handler(3)
